Is it possible to live in New York City decently on $30,000 a year? Details, please.

Of course, it depends on how you define "decently." You're not going
to be eating out every night on that salary, but I suspect you can
indeed live in New York City on that salary, though you might need or
want to (1) live with roommates and/or (2) live someplace other than
Manhattan, where rents are (somewhat) cheaper.

Other commenters (or an official researcher) may have more details,
but I've come to think that when it comes to living in New York, when
there's a will, there's a way. $30,000/yr is not a great salary for
living in the big city, but plenty of people manage to live there on
that much or less.

Before you start looking for an apartment, you need to make an
important decision: how much are you willing and able to pay in
monthly rent? In a city as expensive as New York you will probably
have to spend a large percentage of your income on housing. A good way
to find your upper-limit for housing costs is to divide your monthly
net (after tax) income by three. If this figure seems unusually low,
you have three options: (1) make more money, (2) consider living in a
less expensive area, like Queens, Brooklyn or Hoboken, or (3) save
money on rent by finding a roommate.
also if you are looking for a apartment how many bedrooms and what
area you want to live in all this information is important before we
can really say if it is possible.

There are plenty of people who live on the city on less than that. 
Don't expect a two bedroom apt. on Park Ave.  Look hard enough and you
can find a place.  As for living expenses (food, clothes, etc.) there
are bargains to be found.  Many books have been written on the
subject.